How to use dovetail spacing layout
What this calculation does
This dovetail layout spaces equal tails between equal inner pins and end half-pins, then converts the selected slope ratio to an angle.
Measure joint width, choose tail count and pin widths, and enter the run-per-rise slope ratio you selected.
Enter the measurements
- Board width across the joint: Measure board width across the joint.
- Number of tails: Choose the number of equal tails.
- Width of each inner pin: Choose width for each inner pin.
- Half-pin width at each end: Choose the half-pin width at each edge.
- Tail slope ratio (run per rise): Enter horizontal run per unit rise.
Formula and variables
Tail width = (board width − (tail count − 1) × inner pin width − 2 × end half-pin width) ÷ tail count. Slope angle = atan(1 ÷ entered run-to-rise ratio).
Tail width is remaining board width after pins divided by tail count. The slope angle is atan(1÷run-to-rise ratio), converted to degrees.
Read the result
An 8 in board with four tails and the stated pins leaves 1.75 in per tail; a 1:8 slope is about 7.125 degrees.
Worked example
Inputs: 8 in board, four tails, 0.25 in inner pins, 0.125 in end half-pins and 1:8 slope
- Tail width = (8−3×0.25−2×0.125)÷4 = 7÷4 = 1.75 in.
- Slope = atan(1÷8) ≈ 7.125°.
Expected result: 1.75 in tails and 7.125° slope
Frequently asked questions
Is 1:8 a required dovetail slope?
No. The slope is a user-selected design choice, not a universal strength rule.
Does this mark the mating pins?
No. Transfer the pattern and verify orientation on the mating board.
Conditions, presets and technical notes
This is one symmetric pattern with equal tails, equal interior pins and equal end half-pins. The slope ratio is a user design choice, not a universal strength rule. Check mating-board orientation and actual marking convention before cutting.